1. Field of Invention
This application claims priority to U.S. patent application Ser. No. 60/215,377, filed on Jun. 29, 2000. This invention relates to communications systems. Specifically, the present invention relates to systems and methods for detecting DTX frames in communications systems.
2. Description of the Related Art
Cellular telecommunications systems are characterized by a plurality of transceivers in mobile phones and base stations. Each transceiver includes a transmitter and a receiver which communicate over a channel.
One approach to increasing the information-carrying capacity of the channel is to enhance the signal-to-interference ratio (SIR). The SIR is often expressed as a ratio of the energy per information bit received to the interference density of the received signal. To increase system capacity, the transceivers operate at low signal-to-interference ratios (SIRs). As an alternative, the SIR of the channel can be increased. To increase the SIR, the power of the transmitted signal is increased by a signal from the receiving transceiver. However, increases in transmitted power lead to increases in interference to other mobiles and thereby limit the capacity of the channel. In addition, increases in transmitted power levels increase power consumption (particularly problematic at battery powered mobile units) and reduce network throughput. Accordingly, it is generally desirable to operate the system at an optimal transmit power level that balances signal-to-interference considerations with power consumption, throughput and system capacity considerations.
As will be appreciated by those skilled in the art, data is transmitted in intervals referred to as ‘frames’. In accordance with the new IS2000 cellular standard, a base station can assign more channels to the mobile and transmit on the supplemental channels. However, if the base station has no data to transmit, under the new standard, instead of de-assigning the channel, the base station just reduces the signal gain. This is referred to as a ‘DTX’ mode and frames transmitted in this mode are ‘DTX’ frames.
Unfortunately, the effort to operate the system at optimal transmit power levels is impeded by the transmission of DTX frames. The receiving unit demodulates the data bits in the frame, monitors power over the frame, checks the quality of the frame, and performs CRC (cyclic redundancy check) error checking. If the CRC check fails, bit errors are assumed the receiver erases the frame and sends a signal to the transmitter to increase the transmit power and resend the frame.
Accordingly, when the receiver receives a DTX frame, it attempts decode the frame, a frame of noise and interference. This causes the receiver, i.e., the mobile unit, to send plural erased frame signals to the base station. In response, the base station increases the power set point for the mobile, which increases power consumption while reducing network throughput and capacity.
Conventional systems and methods for rate determination and detection of erasure look at each frame individually and have heretofore offered limited performance. Accordingly, a need remains in the art for a system or method for distinguishing between DTX frames and frames with high bit error rates suitable for erasure in the transmission of data between a base station and a mobile unit in order to achieve optimal transmit power levels.